This invention relates generally to fabrication of layered composite materials, and more specifically, to methods and systems for automated ply boundary and orientation inspection.
In some current production situations, the fabricator is required to inspect 100 percent of the ply placements for a composite structure using optical laser templates (OLT). While it is possible to use other large scale metrology methods, such as laser radar, OLT is currently the most efficient method of inspection. With certain structures, this inspection process takes, on average, between thirty and ninety minutes per ply. These structures may include sixty to seventy or more individual plies. As is easily understood, this OLT inspection turns out to be a significant portion of the total flow time utilized in the fabrication of the structure, which in certain instances may be a composite fuselage barrel for an aircraft. While this may be acceptable in a prototyping environment, it is not acceptable in a manufacturing environment. In an increased production rate environment, the task of inspecting ply boundaries utilizing the OLT process greatly inhibits the rate capabilities of a production facility. In addition, as the composite structures may be modified, for example, a stretched version of the composite fuselage, the OLTs may not have the capability to project at a needed accuracy over an enlarged surface.
As described above, OLTs are the currently preferred method of inspecting ply boundaries and the orientation of individual plies. After each ply is placed with, for example, a fiber placement machine, OLT units are indexed to a cure mandrel and the appropriate ply is projected onto the surface of the composite structure currently being fabricated. After a projection is established, an inspector visually compares an edge of the projected ply boundary to an edge of the recently placed composite ply. Any areas of question are measured and reworked. When working with a large structure, such as the full surface of a fuselage barrel, an angle of incidence issue arises. Specifically, due to a limitation on the angle of incidence between the laser projection and the part surface, a full fuselage ply must be projected onto in multiple (e.g., at least six) segments of the OLT to cover the full circumference of the fuselage.
As mentioned above, the current OLT process is time consuming. On average, thirty or more hours are attributed to inspection of ply boundary and orientation for a full fuselage part, which is unacceptable in a high rate of production environment. In addition to the throughput rate limitations of the current OLT system, there are some technical limitations as well, such as the angle of incidence problem described above. When a single OLT is pushed beyond its operating capabilities, either part tolerances have to be relaxed, multiple OLTs augmented by metrology systems have to be utilized, or an alternative ply boundary verification system will need to be used. Currently, there is no more acceptable and cost effective process for inspecting ply boundaries than OLT.